This invention relates to the use of macromer-forming catalysts in the formation of macromers, especially the macromers used to make ophthalmic lenses.
Ophthalmic lenses such as contact lenses are often made in polymerization processes which employ initiators. Acylphosphine oxides are a useful class of initiators for free radical polymerizations of the type frequently used to make ophthalmic lenses. Bisacylphosphine oxides and their use are described in U.S. Pat. No. 5,534,559 incorporated herein by reference. All of the patents and patent applications listed herein are incorporated by reference. Unfortunately, the prior art macromer-forming catalysts which are used in the preparation of the macromers, which are used to make ophthalmic lenses, often adversely effect the stability of these initiators and the use shelf life of the multicomponent formulations which contain them.
It is often desirable to prepare a mixture of materials together with one or more macromers, one or more initiators and other additives that will ultimately form the lens upon completion of curing. These types of mixes are referred to as the “monomer mix” in this specification.
Stability of the initiator can effect the shelf life of the monomer mix. Increasing the “shelf life” or stability of the monomer mix from that seen in the prior art is desirable since it reduces the need to frequently prepare monomer mix lots (as described below) and the possibility of introducing lot to lot and intra-lot variations in lens production.
Unfortunately, in the prior art initiators tend to be unstable in a variety of environments lessening their potential. EP 849,296 proposed a method of stabilizing bisacylphosphine oxide initiators used in the production of urethane (meth)acrylate polymers used for optical fiber coatings. The method involves preparing a urethane (meth)acrylate oligomer using a tertiary amine catalyst and then mixing with the photoinitiator and other coating formulation components. There are also similar methods in the prior art of stabilizing monoacylphosphine oxide photoinitiators in the presence of a tin compound used as a macromer-forming catalyst in the urethane (meth)acrylate oligomer synthesis. U.S. patent application Ser. No. 01/09,076 teaches the use of tin catalysts with acetic acid.
Unfortunately, a tin catalyst such as dibutyl tin dilaurate (DBTDL) is not desirable when applied to monomer mixes used to make ophthalmic lenses because of the potentially deleterious effect it has on the photoinitiator and may have on various other components of the monomer mix. This is particularly true where the monomer mix is used to make silicone hydrogel lenses.
The prior art teaches the use of Lewis acid catalysts, including, but not limited to, tin catalysts, such as DBTDL for the formation of macromers. The decrease in initiator (especially photoinitiator, particularly bis-(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (DMBAPO)) concentration after mixing into a monomer mix results in the production of lenses having unacceptable parameters and physical attributes. Therefore, a new type of macromer-forming catalysts, which does not effect initiator concentration, is desirable.